Leicester City’s Wes Morgan, left, and Chelsea’s Diego Costa battle for the ball in the game on Monday night.
Photograph: Mike Egerton/PA

There was a moment early in the second half on Monday when Wes Morgan jinked inside Pedro then found himself faced with Diego Costa. Through some sleight of the upper body, Morgan persuaded Costa to go clattering into space to his left and strolled away. This was Wes Morgan, the same Wes Morgan who last year became a byword for haplessness, a series of errors and moments of misfortune culminating in the moment when he slid helplessly across the turf against Liverpool and saw a penalty awarded as a cross hit his face.

Claudio Ranieri laughs last with José Mourinho looking far from special | Stuart James

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After Loïc Rémy had pulled one back, it was easy to imagine Chelsea pounding away until Leicester crumbled. Their threat in what, with injury time, turned out to be the 18 minutes that remained, was only intermittent. Morgan won header after header, a figure of fun turned into a tower of strength.

Claudio Ranieri pointed out afterwards how well Andy King and Gökhan Inler had played after coming off the bench and spoke of the spirit at the club: “We are a friendly team.” There is a togetherness, he says, that extends to the backup. Inler, even with his injury problems, cannot have expected to be kept out of the team by Danny Drinkwater and N’Golo Kanté, so if that is true it says much for the atmosphere Ranieri has created.

In the context of Monday, it is impossible not to make the comparison with Chelsea. At one point Diego Costa raged at the defence, while there is obvious tension between José Mourinho and Eden Hazard. It is easier to project an upbeat team spirit, of course, when a side is winning but even then it is hard to pretend his is a happy Chelsea camp.

Mood is one of those intangibles in sport. The more fundamentalist statistics wonks deny morale or confidence any role – even though, as anybody who has ever played sport at any level knows, there are days when it at least feels as if you cannot miss – or will make every save or take every catch, or whatever – and days when it feels as if you will fluff everything.

One of the favoured tools of football analysts these days is expected goals. Essentially, it assesses a team’s chances in terms of quantity and quality, and works out how many goals a team “should” have scored in a game. Arsène Wenger referred to it recently when explaining why he had moved Aaron Ramsey into a central role – and the metric also suggested Swansea City’s results were better than their performances before the slump that cost Garry Monk his job.

According to the Dutch website 11tegen11, Chelsea should have won 2.22-0.77 on expected goals. And that’s where mood becomes so important: once Leicester had gone ahead there was never a moment of the game when it seemed that Chelsea might win. It is true they rallied in the final half-hour and that the switch to a back three led to pressure on the Leicester goal but even after Rémy’s strike, the expectation of a gathering storm soon dissipated. Leicester just looked slicker, sharper, more inventive, more incisive; Chelsea were ponderous, almost visibly overthinking every action.

Once Leicester had gone ahead there was never a moment of the game when it seemed that Chelsea might win

Mourinho has spoken of Costa’s lack of confidence and the impact that has had, not only on his capacity to convert chances but also on his movement; out of sorts, Costa drops deep, Mourinho explained, away from the area where he is at his most dangerous, which was one of the reasons Chelsea looked more threatening once Rémy had come on to given them a presence in the box. Mourinho, though, was reluctant to countenance the idea of doing that regularly because of the impact an additional forward would have on the midfield.

Costa’s lack of form raises questions about Chelsea’s recruitment. Rémy is not a like for like replacement, being far more effective in a front two – which was one of the reasons Harry Redknapp, before Rémy was sold, tried to introduce a back three at QPR after their promotion – like Mourinho on Monday, he reasoned the best way of getting a front two without sacrificing something in the centre of midfield was to withdraw a defender. Signing Radamel Falcao, given his form last season and his recent injury record, was, at the very least, a major risk. The consequence is that Mourinho, given his reluctance to select youth players, has no option but to pick Costa.

Mood, however, is not only a problem for strikers. What was it that caused Kurt Zouma to allow Jamie Vardy to dart in front of him to convert Mahrez’s cross? It is a lapse that would be culpable at any level, all the more so given it seems a fair assumption that that sort of run was one of the four scenarios for which Mourinho had prepared his team. What is that? Confidence, a lapse of concentration, a lack of edge?

In some ways it is understandable Mourinho spoke of feeling “betrayed”. After all, if he has prepared his side specifically for that type of mood and they still make that sort of error, what else can he do? Yet at the same time, he has to bear responsibility for that mood and telling players they are betraying him seems more likely to breed resentment than to provoke a positive response.

Diego Torres’s biography of Mourinho was controversial and much-contested but, as time goes by, the parallels between what he describes happening at Real Madrid and what is happening at Chelsea become more and more striking. That betrayal line seems a classic case of the process by which Mourinho distances himself from failure, deflecting the blame on to others.

The contrast with Ranieri and his relaxed and self-confident Leicester City could hardy be more striking. This is the revenge of the friendly uncle. Eleven years after being replaced by Mourinho for not being ruthless enough, Ranieri finds himself 20 points above him in the table.